Marginocephalia
The Marginocephalia are a clade of ornithischian, or bird hipped, dinosaurs that evolved in the Late Jurassic and achieved their zenith in the Late Cretaceous. They are found mainly in Asia and North America, but a couple of genera have been found in Europe and possible remains in Australia, suggest they were far more widespread. The Marginocephalia are divided into two groups; the Ceratopsians and the Pachycephalosaurs. The Ceratopsians were a diverse group of herbivores, though they all had two uniting features; a rostral bone or beak and batteries of chewing teeth behind the beak. Primitive forms could be bipedal but more advanced forms were purely quadrupedal. Many also had frills that acted as supports for the jaws and also display features. The more advanced forms also had impressive horns which were used for display, defending territory and maybe for defence against carnivores. The Pachycephalosaurs were purely bipedal and relatively small in size. They retained primitive features, such as small, simple peg like teeth which were worn down over time and then replaced. Later genus had layers of thick done of bone over their skulls and crowns of small hornlets around the dome. These domes were used in combat between males by hitting their flanks. The oldest members of the ceratopsians were small bipedal herbivores, including Pisttacosaurus and the Jurassic Chaoyangsauridae. These dinosaurs possessed the ubiquitous beak of the family but they either lacked or had tiny crests. Some also had small horns on their cheeks and long filaments on the tail, similar to those found on Heterodontosaurids. It is likely other more advanced ceratopsians had these also. The ancestry of the Pachycephalosaurs is unclear, as fossil remains of pachycephalosaurs are generally rare and faults in identification are common. For example the dinosaur Yaverlandia from the Isle of Wight, which was named after the discovery of a piece of skull and assumed to have been a pachycephalosaur, was later found to have belonged to a small therapod. Several other well known genera such as Stygimoloch, Homalocephale and Dracorex have recently been thrown into doubt and some palaeontologists now class them as juveniles of larger genera such as Prenocephale. Currently the oldest confirmed Pachycephalosaur known is Acrotholus which lived in North America during the early stages of the Late Cretaceous. The enigmatic ornithopod Stenopelix from Earliest Cretaceous Germanyis also a candidate for the earliest pachycephalosaur, but may in fact be a late surviving Chaoyangsaurid. The ceratopsians were adapted to feed on tough plants such as ferns and conifers, while it seems pachycephalosaurs evolved to take advantage of the softer leaves and fruits of the newly evolved flowering plants. Both families were herding animals and may have also displayed sexual dimorphism; with males being bigger, with larger horns or domes and possibly brightly coloured during mating. They also displayed maternal care for their young, as seen in therapods and hadrosaurs. In Prehistoric Kingdom So far in Prehistoric Kingdom, a total of six Marginocephalia have been announced; one Pachycephalosaur, one basal member of the Psittacosauridae and four Ceratopsians. Psittacosauridae * Psittacosaurus Pachycephalosauridae * Prenocephale Ceratopsians * Pachyrhinosaurus * Protoceratops * Styracosaurus * Triceratops